1. Field of the Invention
The present invention relates to a device for anchoring in and/or reinforcing hard materials, such as stone, concrete and the like. The device consists of a continuous body, made in one piece designed for insertion axially into a hole in said materials and which has, transverse to its axis, expansible gripping surfaces or points arranged so as to, when expanded, bear against and engage the sides of the hole for anchoring the device into the hole.
2. The Prior Art
The mechanical anchoring of objects into very hard building materials such as stone, brick and concrete, usually requires a prebored hole of a diameter suitable for the gripping surfaces. An exception is hard steel studs or nails, which may only be driven by very great force from, for example, an explosive-operated stud gun.
Hole-mounted anchors, however, of several different kinds are to be found. A common type are plugs of various constructions, the gripping surfaces or points of which are designed to be forced against the hole walls by the driving of a conical screw. Also, there are various kinds of expansion bolts where one or more sleeves or segments are forced to expand into conical surfaces by a turned bolt. Other constructions can be likened to split sleeves or spikes which are axially displaceable from each other, while others can again be cylindrical, sprung tube segments with special configurations. Furthermore, there are angled loops or wires with a hooking grip against the hole walls.
Another construction, intended specially for reinforcement purposes, is in the form of a deformable tube so constructed that it can be made to expand by a high internal hydraulic pressure.
None of the known anchors or reinforcing members fulfill the demands which could reasonably be made upon a theoretically objection-free and optimum anchoring or reinforcing device for hard materials. Among reasonable demands and requirements, the following properties ought to be specified:
The device should, with the cheapest possible manufacture in mind, consist of a single component without the need for intermediate assembly or the like. It should require a minimum of resources and be simple to mass-produce, thus creating the conditions for a low purchase price for the end user.
The device should also be easy to install and remove on site and should not require any major professional expertise.
The construction principles should be such that the device becomes self-locking, which means that the gripping force should increase upon an increased pulling force.
Through construction and choice of materials, the device should have good static performance and high tolerance to vibrating or pulsating loads.
To function most effectively the distribution of pressure against the hole walls should be spread over a large area and be uniform along the entire length of the hole.
Normal cavities in the material, for example in hollow blocks, should not result in an absence of gripping force.
To reduce the cost of and to limit stock and assortment, the device should be versatile in its uses and universal in its function. It should also allow the use of extensions and accessories of various kinds.
With regard to safety and reliability, the device should be fire and temperature proof and also resistant to corrosion and ageing.
Finally, it is in many cases advantageous if the device used can to some degree compensate for small errors in centering which occur during drilling, especially when hammer-drilling in heavy stone material.